Process of preparing laminated material



Patented Apr. 28. 1942 PROCESS OF PREPARING LAMINATED MATERIAL Donald Edwards Edgar, Philadelphia, Pa., assign or to E. I. du Pont de Nemours '& Company, Wilmington, Del., a corporation of Delaware No Drawing. ()riginalapplication June 23, 1934,

Divided and this application May 1, 1940, Serial No. 332,687

Serial No. 732,083.

14 Claims.

Thisinvention relates to adhesivecomposltions, and more particularly, to heat energizable compositions comprising a synthetic resin and a cellulose nitrate.

This application is a division of my applica-.

tion Ser. No. 732,083, now Patent No. 2,234,236,

which is a division of my prior application Ser. No. 658,270, now Patent No. 2,064,802.

An object of the present invention is to provide adhesivecompositions comprising a thermoplastic synthetic resin and cellulose nitrate, which adhesive compositions are heat energizable and do not depend upon evaporation of solvent for obtaining a suitable bond. A further object is to provide an adhesive composition which does not require high temperatures to secure thermohardening to give'a' suitable-bond and which is not dependent on any chemical'change for the ther object is to provide such an adhesive which is initially and permanently flexible and is substantially inert so that it is not appreciably affected by normal temperatures or exposure to the air.

- Another object is to provide a heat. energizable adhesive which will give a bond not softening under conditions of normal or slightly elevated temperatures, so that slippage of the cemented surfaces does not take place. v

A still further object is the provisionof a heat energizable cement which is sufiiciently elastic so that differences in the coefiicient of linear expansion of two dissimilar materials which are ferred form of the adhesive of the present invention comprises a cellulose nitrate having a modified by an agent from. the group" consisting of vegetable drying and semi and non-drying oils, stearic acid, oleic acid,- and higher alcohols suchas butyl, and amyl alcohol, et cetera, dispersed in a suitable splvent mixture.

The following examples are given to illustrate the inventioni Example 1 Per cent Cellulose nitrate (approximately 4 sec. viscosity 8.2 Denatured alcohol 10.0 Toluol 29.0 Dibutyl phthalate -l 6.4 Ethyl acetate 33.0 Synthetic resin 13.4

Example 2 Per cent Cellulose nitrate (approximately 2 sec.

viscosity)- 8.2 Denatured alcohol 10.0 Toluol i 29.0 Ethyl acetate 33.0 Dibutyl phthalate $5.4; Synthetic resin 13.4

The synthetic" resin in the above examples is a reaction product of:

Per cent- Phthalic anh drifln 45.8 Glycerol y Castor il 100.0 The resin was compounded by charging the above 1!]- redients into an aluminum kettle fitted with a mechanical stirring deviee and a thermometer. The batch was heated up to 225 C. in thirty minutes and held at thls I temperature until an acid number of 13-15 was reached,

stirring being maintained throughout the run.

The heating cycle took about 4 hours.

The viscosities given throughout this specifi- '.cation'are measured in accordance with method outlined in A. S. T. M. Tentative Specifications and Tests for soluble nitrocellulose, designation 1 nitrate in a heat energ'izable adhesive. A prenitrogen content of 10.0 to 12.2% and a poly-,

hydric alcohol-polybasic acid synthetic resin D-301-30T. The nitrogen content'i'o'f the cellulose nitrate in the above examples'fwas 11.8 to

ity of the second.

The "synthetic resin in this formula was the reaction product of Example 3 Ea'ample 6 Per cent Per cent Cellulose nitrate (approximately 2 sec Cellulose nitrate (nitrogen 11.4 to 11.6%) 9.9 viscosity) 82 Denatured ethyl alcohol 5.8 -Denatured alcohol- 10,0 Ethyl acetate Tnlunl 33 2 28 Ethyl acetate 29.0 F Dibutyl phthalate 6.4 Plbutyl re Synthetic resin 13 4 synthgtlcl f 100.0

{ The synthetic resin in this formula was the re action product of Per cent 37 4 Per-cent D h 1 gg g l ic ydnd gg-i 15 pfitaiii in fi ifiim 4m .Glycerine 1 24h Stem L 100.0 100.0 the materials into The resin was prepared as described in Example 1.

This example represents a slight modification of Example 2,- whereby a slight residual tackiness inherent in the composition of Example 2 is eliminated, thus permitting materials coated with the modified composition to be stored with surfaces adjacent to each other without danger of sticlnng. This adhesive composition gives substantially odorless and tasteless films, thus making it quite suitable for use in connection'with food products. .The cellulose nitrate in this ex- The synthetic resin in this formula was the reaction product of:

Per cent Phthalic anhydride 54.3 Gly'cerine 24.2 Castor oil 21.5

This resin was prepared by cha gins all of the ingredients into a kettle and heatinpnto in 1 hours. *This temperature was mainta ed for approxima ely two hours or until an acid number of 73-77'was reached.

a kettle and heating to 1 0-200 The resin was prepared 1) charging C. This temperature was maintained for approximately 4 hours, at the end of which time the acid nurnber'was 40-50.

The "synthetic" resin in this example is the same as that used in Example 6.

Example 8 Per cent Celllose nitrate. (80 sec. viscosity) 11.3 Denatured alcohol 8.6 Dibutyl phthalate 13.5 Toluene i 16.0 Ethyl acetate 19.0 Synthetic" rasinuu 30.7

' The nitrogen content of the cellulose nitrate in Example 5 I Per cent Cellulosenitrate 10 Ethyl acetate 1 p 20. .Toluol 30 Denatured ethyl alcohol 28 Synthetic? resin 12 'The "synthetic resin in this example was the reaction product of:

Per cent Diethylene lyco 41.7 Phthalic an ydride .583

. The cellulose nitrate used in the above two examples (Examples '4 and 5)- had a nitrogen content of'approximately 10.6%.

this example is 11.4-11.6% and the "synthetic resin is the same as used in Example 6. This composition is particularly suited for coating on fabrics and other porous surfaces because of its relatively high viscosity which prevents undesirable impregnation.

Example 9 Per cent Cellulose nitrate (/2 sec..viscosity) j 15.0 Denatured alcohol 15.0 Ethyl acetate 31.0 Dibutyl phthalate 8.0 Tnhinl 15,0 Synthetic" resin 16.0-

The "synthetic resin in this formula is a tolueneed and the mixture agitated until complete so for use.

- and polybasic acids.

lution was obtained. Finally, theresin constituent already dissolved in a portion of the active solvent of the ultimate formula was added and the mixing continued until homogeneity was secured. The adhesive composition was then ready The adhesives described in the above examples are substantially transparent and colorless. It will be understood that these compositions may be colored by the incorporation of a suitable coloring agent, such as a dye or a pigand a cellulose nitrate having a nitrogen content of 10.0 to 12.2%. v p

The viscosity characteristic of the cellulose nitrate is not' critical so long as the nitrogen content is kept'within the specified limits. Cellu- Iose nitrate having a viscosity of below 4 seconds can be used satisfactorily and the upper limit of the viscosity characteristic is only dependent upon the workability of the solution for practical purposes. For application of the adhesive to a non-porous surface, such as metal, glass, regenerated cellulose sheets, and. the like, a low viscosity cellulose nitrate is satisfactory, while for a porous surface, such as fabric and certain papers, a high viscosity cellulose nitrate is more to be desired. Cellulose nitrate having a viscosity of 80 seconds has been found very satisfactory for general application.

The type of polyhydric alcohol-polybasic acid synthetic resin operative in the preferred'form of the present invention can be varied without limit, although certain types of polyhydric alcohol-polybasic acid synthetic resins are much more suitable than others. A resin having the property of being a solvent for cellulose nitrate and having a high coefficient of plasticity",

made therefrom. In place of phthalic acid many other acids, such as malic, adipic, succinic, tri mellitic, dilactylic, fumaric, and sebacic acids can be used in the manufacture of these resins.

Other resins having solvent power for cellulose nitrate and having "high coeilicients of plasticity", for example, aryl sulfonamide formaldehyde resins, such as the toluenesulfonamideformaldehyde resin used in the composition of Example 9, resins, benzenesulfonamide-formaldehyde resins, et cetra, may be used. Other resins such as vinyl acetate resins, vinyl acetate-vinyl chloride resins, and certain phenol-formaldehyde resins and urea formaldehyde resins may be used. The toluene-sulfonarnide resins and the polyhydric alcohol-polybasic acid resins are preferred because of their compatibility and high coeflicient of plasticity. Certain types of this latter class of resins, i. e,, polyhydric alcohol-polybasic acid resins, modified with high molecular weight acids and/or higher molecular weight alcohols, or those from dihydric alcohols, particularly ether alcohols preferably with high molecular weight acids, represent the most preferred embodiment of the present invention because of their embodying the advantageous characteristics of freedom from stickiness, high coeflicient of plasticity, high degree of heat energizability, higher capacity of being resoftened by high temperatures before losing their heat energizability, high compatibility with cellulose 'nitrate, high water resistance, and excellent strength of bond.

,As shown in the examples, the proportion of cellulose nitrate to synthetic resin can be varied widely, depending upon the specific properties desired. A range of 0.6-2.0 parts of synthetic resin to one part of, cellulose nitrate is preferred, but highly useful, adhesive compositions that is, considerable increase in-mobility per degree rise in temperature is most suitable. The

' resins modified with non-drying oils have been found especially advantageous. Cocoanut, cottonseed, hydrogenated cottonseed, and castor oils may be mentioned as non-drying oils of particular merit. Higher aliphatic acids, such as oleic, and stearic, are also very suitable as modifying agents, but it is not preferred to use these acids in amounts greater than 50%. by weight of the resin. Butyl alcohol is an outstanding alcohol modifying agent, but other high boiling alcohols, such as hexyl, propyl, amyl, and benzyl alcohols, cyclohexanol and terpineol are also upon, what properties are desired in the adhesive useful. Resins modified with rosin -or gums,

such as kauri copal, and the like, may be used but they are not as desirable as resins modified with the above disclosed agents.

As is well known in the art, the polyhydric alcohol-polybasic acid synthetic resins may be made from awide variety of -polyhydric alcohols Di-hydric and trihydric alcohols, though preferred, need not necessarily be used, as the higher polyhydric compounds,

such as sorbitol, pentaerythritol, and the like, may also be used. Polyhydric ether alcohols, such as diethylene glycol, triethylene glycol, monoethylin, monobenzylin, diethyl ether of sorbitol, diethyl ether of pentaerythritol, diglycerol, et cetra, are-particularly advantageous because of the high compatibility and high coeilicient of plasticity characteristic of resins may be employed with from 2-5 parts of resin to one part of cellulose nitrate. It is necessary in order to-provide a satisfactory adhesive composition that the synthetic resin'be compatible with the cellulose nitrate, that is, the synthetic resin must not separate from the cellulosenitrate when deposited in coating.

As'shown in the above examples, the use of a plasticizer in these adhesive compositions is optional and dependent, to a considerable degree,

and the type' of synthetic resin employed. For example, if the adhesive composition contains cellulose nitrate and, as a synthetic'resin, diethylene glycol phthalate, or other polybasic acid ester of a dihydric ether alcohol, no plasticizer is necessary, since these resins are of the soft, low melting type and suflicient heat energizability is developed through this medium,

but in other cases where the synthetic resin isof the harder type. the addition of plasticizer is preferred in order to obtain sufilcient heat energizability to provide satisfactory bonding properties at suitable temperatures. plasticizer is used, it should be selected from the so-called "solvent type. that is, a solvent for cellulose nitrate. Such plasticizers as dibutyl phthalate, dibutyl tartrate, tricresyl phosphate, tria'cetin, and ethyl meta-sulfonamide are suitable.

With respect to the solvent mixtures employed in these compositions, their function is simply to provide a suitable vehicle for the film forming ingredients in order that a satisfactory film may be laid and theydo not affect the operation xylenesulfonamide-formaldehyde" a film but give a homogeneous When a r of the composition after the moo has dried out.

The solvents and solvent mixtures which may be employed will readily occur to those skilled in the art.

posit a clear, nearly colorless film. After applying the adhesive to the objects which are to be joined together,. the adhesive film is allowed to dry,,which operation usually takes from 3-20 minutes at room temperature, depending somewhat on the type ,of material coated and the particular composition of the adhesive. Force drying, of course, may be employed. When the solvents of the composition havecompletely evapo rated,.the objects to be cemented together are brought into intimate contact with eachother and heated with a heat press, roll, or fiat-iron. An ordinary electric fiat-iron may be used. A temperature of 130-150" C. is suitable and little pressure is necessary, 2 to 15 pounds per square inch being suflicient, although it will be apparent that greater pressure is desirable. The exact heating time is largely dependent on the conconvenient to employ light pressure andheat.

The adhesive compositions of the present invention, and particularly those employing polyhydric alcohol-polybasic acid resins, deposit films The proportions of ingredients in the solvent mixture and the proportion of solvent which are characterized by a considerable degree 4 of elasticity, excellent initial and retained flexibility and adhesion and have ve y little color, odor, or taste. Furthermore, the bond is waterproof and, unlike rubber adhesives, the adhesive films are, in general, not susceptible to oxidation and are, therefore, of greatly improved durability over films deposited from the .known rubber ad hesives. Since these adhesive compositions do not depend upon evaporation of solvent to set up,

they can be used to advantage between impervi ous surfaces. A particular advantage of these adhesives lies in the fact that when used with .relatively light weight materials, such as paper,

cardboard, regenerated cellulose sheets, and the mum air resistance on the exterior of dirigibles-;-

like, they do not cause warpin g, curling, or stainmost instances; It is believed that the resin component of the adhesive is substantially unaffected by the heat, except where prolonged or a very high temperature is employed, and that practically no polymerization occurs. This is borne out by the fact that the adhesive fihn may be again softened, at least once, after the bond has been effected by-further application of heat. This allow the embossing of bonded materials such as Y.

paper, fabrics, leather, and the like, without destruction of the bond. These properties also are of distinct advantage where two surfaces of dissimilar coefiicients of linear expansion are joined, a successful bond for this purpose being dependent on a slight amount of elasticity or cold fiow. Also materials coated with the adhesives of the present invention may be stored for extended a periods without danger of sticking together and without loss of adhesive qualities, 'so that they may be united at any desired time upon the application of heat and pressure.

While there are many uses for the adhesives I herein described, which will readily occur to those skilled'in the art, a partial list of uses for which these adhesives have been found particularly adapted is given below:

l. Regenerated cellulose sheets (plain or moisture proofed) to fabric, paper, cardboard, metal tanks in order to make them more, resistant to the solution stored in the tank;

2. For coating the outside of petroleum field:

tanks and various other tanks in order to obtain the maximum reflection of heat and hence minimum evaporation losses as well as to supply a durable coating, particularly resistant to corrosion by sulfur gases;

3. For coating pipe lines, particularly buried.

pipe lines;

4. For coating cables, particularly underground cables;

5. For obtaining a durable, minimum air resistant coating for fabric used on aeroplane wings andfuselage;

6. For obtaining a durable coating. with mini- 7. For coating both the inside and outsideof refrigerators;

8. For use as a substitute for gold-heaters skin, and other uses where a very impermeable,

light weight, flexible materialls necessary;

9. For coating wood shingles in; order to make them more durable- 1 These adhesives are also particularly useful for impregnating paper, fabric, and similar materials which are subsequently used betweentwo surfaces whichare to be united. The employ- I ment-of these adhesives for cementing surfaces asansss Y impermeable to the passage of solvent vapors, such as metal to metal, moisture proof regenerated cellulose sheeting to moisture proof resenerated cellulose sheeting. and the like, is very advantageous due to the fact that the setting up of the present adhesives is not dependent 5. As a new article of manufacture a layer of thin, flexible, non-porous material securely Joined to another surface solely by means of- .a

. thermoplastic cement comprising a cellulose derivative and from 0.6 to 5 parts of a synthetic resin compatible therewith for each part of celupon evaporation of solvents. It will be apparent to those skilled in the art that most adhesives cannot be used for such purposes, as they depend upon solvent evaporation. Also, these adhesives are of particular advantage in cementing Celluloid, cellulose acetate silk, and

the like, to metal or other surfaces. because the adhesive can be applied to the metal only, then on drying, the Celluloid, cellulose acetate silk, etc.,,can be united to the metal by heat and pressure without being brought into contact with the solvents in the adhesive, which would deleteriously affect the Celluloid, etcetera.

As many apparently widely diil'erent embodiments of this invention may be made without departing from the spirit and scope thereof, it

is to be understood that the invention is not limited to the specific embodiments thereof-except as defined in the appended claims.

I-claim:

1. In the process of preparing laminated materials wherein thin, non-porous sheets are joined by means of a thermoplastic adhesive, the improvement which comprises applying to at least one surface of one of the sheets as the.

sole adhesive a thermoplastic adhesive composicontainsl part of cellulose nitrate and between tion comprising a cellulose derivative and from 0.6 to 5 parts .of a synthetic resin compatible therewith for each part of cellulose derivative,

allowing the film to dry. and uniting the said surface to a second surface by means of heat and pressure.

2. The process of claim 1 in which the resin is an alkyd resin.

3. The process of claim 1 in which the resin is a vinyl resin.

4. The process of claim 1 inwhich the resin is a toluenesulfonamide-formaldehyde resin.

.6 and 2 parts of a sy'ntheticresin.

11. The article of claim 5 in which the adhesive contains 1 part of cellulose derivative and from .6 to 5 parts of resin compatible therewith and being soft and adhesive-eta temperature between C. and C. under a pressure of 2 to 15 pounds per square inch. I

12. The article of claim 5 in which the non porous surface is regenerated cellulose.

13. The article of claim 5 in which the non- I porous surface is metal foil.

14. A laminated materal comprising at least 7 one non-porous surface Joined to a second surface by means of the residue of a thermoplastic cement having approximately the following composition:

. Percent Cellulose nitrate "a 8.2 Diluen 39.0 Active solvent 83.0 Solvent'plasticizernefi-..- 6.4

Thermoplastic synthetic resin 13.4

DONALD E. EDGAR 

